Conventional ski boots as presently used in downhill skiing typically comprise a rigid exterior lower shell member, a relatively stiff upper cuff member and a relatively soft interior liner. The shell and cuff members are generally designed to provide physical protection and mechanical support for a foot, ankle and lower leg and to provide a stable means for releasably securing the boot to a ski. Specifically, the lower shell and cuff members are constructed to provide a restraint against excess sideways and rearward bending at the ankle while providing limited forward bending of the leg relative to the foot. Frequently, depending on the intended use of the boot and often on the ability of the skier, the cuff member of the boot is pivotally connected to the lower shell member so as to permit a limited degree of forward and rearward lean or bending of the lower leg relative to the foot. More advanced skiers frequently use boots constructed without a pivoting cuff member and, in those cases, forward bending is restricted or permitted to a limited extent by a provision for a separation of the upper forward section of the cuff member. The interior liner is provided for warmth and general comfort and, as will be seen, also to adapt a single shell design and size to feet of various shapes and sizes.
The manufacture of the relatively rigid shells and cuff members and the molds for fabricating them are expensive. Because of this expense, manufacturers have resorted to the use of various types of liners that attempt to accommodate a wide range of foot sizes and shapes such as a splay or wide forefoot, wide base, angulated heel, halux valgus, bony prominences, spurs, high longitudinal arch or one foot in size variance with the other foot. Among the constructions used for liners there are included molded and sheet foam rubber, urethane foam, wax, cork, plastic beads and other various flow materials. Indeed, the number of different materials and constructions employed is indicative of the difficulty of the problem of fitting sport shoes in general and ski boots in particular and the unsatisfactory results that have been achieved heretofore. One of the principal reasons is that conventional boots and conventional liners do not provide adequate adjustment for comfort and restraint under all skiing conditions.
A well designed ski boot should not only provide warmth and comfort; it should also provide adequate restraint and a fit which varies in accordance with the dynamic conditions that prevail in downhill skiing. With conventional boots, during a turn, when skiing on packed snow, forward bending at the ankle is usually accompanied by a tendency for hind-foot upward movement and forefoot sideways movement because ski control in turning is usually accomplished by downward and sideways force applied to the forward leading edges of the skis. In powder snow, the forward leading edges are kept raised for planing on top of the snow with a tendency for forefoot upward and sideways movement. When maneuvering in snow of different consistencies, or in bumpy or mogly terrain, the skier alternates frequently and rapidly between forward and rearward leaning in the boots. When, under such conditions, excessive foot movement occurs in a boot, ski control is significantly reduced. In most injury-producing fall conditions, such excess movement also reduces energy transmission between the foot and the release binding, thus impairing a release.
To avoid excessive movement of a foot in a ski boot, skiers, heretofore, frequently were forced to overly tighten the boot by tightening the buckle fittings and by wearing larger and thicker socks or purchasing boots which were too small. Because of the rigidity of the boot shell, the tight fits frequently resulted in uncomfortable pressure areas because of the consequent distortion of the relatively rigid shell. The tight-fitting shell and liner also impaired blood circulation in the foot which resulted in coldness and fatigue.